The present invention relates to both a method of plastically working the outer race of a Birfield type constant-velocity ball joint and a method therefor.
The working of the ball rolling grooves (which will be shortly referred to as the "groove") of the outer race in the Birfield type constant-velocity ball joint has been performed both in a machining manner and in a plastic manner according to the prior art. In the case of the machining manner, the groove itself is not machined before a center hole and a face for providing a reference for the axial position of the groove center (which face will be shortly referred to as the "axial reference face") are machined in advance. In this case, however, there arise problems that the yield is not acceptable, that it takes a long time to effect the machining, and that the lifetime of a cutting tool for machining the groove is short. Therefore, a trial has been made to plastically work the groove. However, since the groove has a shape unsuitable for providing the working reference even if it is worked highly precisely, a sufficient precision cannot be achieved even if the inner spherical surface, the shaft or the like is machined according to the groove reference. As a result, another working reference is provided to effect the cutting operations of all the work portions including the groove.
Therefore, if the working references (i.e., the center hole and the axial reference face) can be worked highly precisely in the groove which has been precisely shaped by the plastic working process, then the cutting process of the groove can be omitted, and still the better even the grinding process of the groove can be abolished, as the case may be.
However, the plastic working process according to the prior art has failed to suffice the aforementioned desire.